Method of making copper alloy products



United States Patent 3,545,074 METHUD OF MAKING COPPER ALLOY PRUDUCTS George S. Foerster and Garth D. Lawrence, Midland,

Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed July 29, 1968, Ser. No. 748,176

Int. Cl. 1323p 17/00, 25/00 U.S. Cl. 29-527.7 6 Claims ABSTRACT OF THE DISCLOSURE A method of preparing copper alloy products which comprises dissolving solid insoluble elements or compounds in molten copper or copper alloy in an amount suflicient to provide upon solidification from about 1 to about 30 percent by volume of dispersed second phase; rapidly solidifying the resultant copper alloy, thereby forming pellets; and working the pellets to form a copper alloy product.

BACKGROUND OF THE INVENTION Field of the invention Prior art A major reason for using copper in a wide variety of applications is its good thermal and electrical conductivity which is at a maximum, in the pure or unalloyed state. However, copper is relatively weak in this condition. Conventionally copper has been strengthened by the addition of solid solution hardeners such as one or more of the metals zinc, tin, silicon, and aluminum in various combinations and various proportions. Copper alloys have been further improved by the addition of elements such as beryllium or mixtures such as aluminum and iron whereby precipitation hardening takes place, normally during heat treating of the solidified metal. Such metals are sometimes called age hardeners when added to copper. However such alloy additions, or merely working the unalloyed copper, significantly reduces the conductivity. Furthermore, the strengthening afforded by these conventional techniques is rapidly lost at elevated temperatures.

Considerable attempts have been made to produce a dispersion hardened copper alloy, i.e., an alloy having stable, micron sized second phase particles. The conventional method of dispersion hardening is to simply mix the solid insoluble particles with copper powder, compact the mixture, and hot work the compact. However, in order to achieve the desired dispersion hardening effect, the second phase particles must be extremely small. Thus, heretofore dispersion hardening of copper and copper alloys has been very difficult and expensive.

A primary object of the present invention is to provide a method for strengthening copper at room and elevated temperatures Without serious loss of conductivity characteristic of the conventional method. A further object of the present invention is to provide an improved method for dispersion hardening copper alloys.

Patented Dec. 8, 1970 ICC SUMMARY OF THE INVENTION These and other objects and advantages are obtained in the method of the present invention which comprises: dissolving in molten copper a sufficient amount of dispersion hardening material to provide upon solidification from about 1 to about 30 percent by volume, ordinarily from about 2 to about 20 percent by volume, and preferably from about 4 to about 10 percent by volume, of solid insoluble second phase in the copper matrix; rapidly soliditying the resultant molten copper alloy, e.g., by atomizing, to form pellets; and Working the pellets to produce a high strength wrought copper alloy product. Such product has realtively high room and high temperature strength properties, thermal conductivity and electrical conductivity.

Dispersion hardening is differentiated from precipitation hardening on the basis that the second phase formed on dispersion hardening (1) generally separates during solidification of the alloy, though it may separate from under cooled supersaturated solid solution as a consequence of working the alloy, (2) is comprised of particles having dimensions in the micron range rather than the Angstrom range, and (3) is substantially not solid soluble in the matrix metal during conventional heat treatment of the alloy; therefore agglomeration tends to be mineral.

The dispersion hardening material should have appreciable liquid solubility but limited solid solubility and/or diffusivity so that after hot working, exposure to high temperatures, or solution heat treatment of the dispersioned hardened metal, the dispersion hardening material, once intimately dispersed in the solid metal, remains uniformly dispersed as particles less than about 5 microns in diameter, and preferably less than about 1 micron in diameter. The term diameter is intended to refer to the longest dimension of the particle in the event that the particle is not equiaxed. The most preferred dispersion hardening materials are compounds that are stable in the matrix or base metal, have very high melting temperatures, but have limited solid solubility.

The second phase should be stable, i.e., it should agglomerate relatively slowly if at all in the copper alloy. Materials that have high melting temperatures, above about 2500 F. and preferably above about 3000" F., tend to be stable. Another indicator of stability is solid solubility, which should be below about 2 atomic percent and more preferably below about 1 atomic percent. Also, the second phase should not significantly depress the solidus of the copper or copper alloy in order not to impair hot workability or maximum service temperature.

For purposes of the specification and claims, compounds formed by a metal and metalloid are herein referred to as intermetallic compounds. Such compounds may be added per se to the molten copper or formed in situ. Chemical compounds such as Cu O may also be formed in situ. The dispersion hardening material, whether it is functioning as an elemental substance, intermetallic compound, or other compound, should have suflicient liquid solubility to permit incorporation of useful proportions in the molten copper. Therefore, liquid solubility should be at least 1 atomic percent and preferably at least 3 atomic percent.

Broadly speaking, the addition to the copper source, i.e., copper or copper alloy, of dispersion hardening material in the form of one or more chemical elements or compounds in an amount that is miscible with the molten alloy but forms a second phase on solidification of the alloy or as a consequence of subsequent working, brings about the desired strengthening of the copper alloy and thorough dispersion of the second phase according to the invention. The solid solubility of the second phase may be exceeded because the addition solubility per se has been exceeded, or on account of interaction between different elements constituting the addition, or between the addition and the copper of the alloy, to form one or more compounds present in an amount in excess of solubility thereof.

Suitable elements for addition to form copper compounds of limited solid solubility include for example cerium and other rare earth metals and mixtures, thorium, zirconium, boron, calcium, and sulfur. Such elements have 4 ally to be avoided since some surface oxidation of the pellets may occur. Such oxidation tends to interfere with bonding of the pellets during subsequent compacting and working.

The pellets can then be worked by extrusion, forging, or other conventional pellet fabricating techniques at room or elevated temperatuers to form a copper alloy product characterized by a fine second phase dispersion in the copper matrix, i.e., a dispersion hardened copper base alloy. Preferably the pellets are worked by extrusion.

a solid solubility in copper below about 2 atomic percent. The present invention provides a method of preparing Elements that react in copper to form a phase having a dispersion hardened copper alloy having the desired limited solid solubility are tabulated in the following characteristics of both room temperature and high tem- Groups I and II. Each of the elements in Group I react perature strength with adequate conductivity. This copper with most of the elements in Group II to form the desired alloy product is obtained without employing the exphase and vice versa. tremely fine powders conventionally used with their attendant difficulties. Group I! Group Ii! The following examples serve to illustrate the inveng f ss ln' tion and are not intended to limit the scope thereof.

1rcon1um 1 icon Rare earth metals Phosphorous EXAMPLE 1 Scandium Arsenic A melt of a copper alloy containing 0.53 weight percent Yttrium Antimony misch metal (Example 1) was prepared and jet atomized Calcium using an argon atmosphere to form pellets passing through t a 100 mesh screen. The pellets were cold compacted Examples of stethie intermetaiiie Compounds suitable in a 3 inch extrusion press container and heated to 1000" for dispersion hardening according to the method of the F. However, the compact could not be extruded into Present invention and formed of the Consequences of /2 inch diameter rods using 500 tons extrusion pressure. slleh interactions are! s z s s Cesh, and z- The hot pressed billet was'ejected, cooled and machined Preferred additions that bring about dispersion hardto fit into a 2% inch 1 X 1 Copper tube The e in the pp or pp base alloy included, for canned alloy was then heated to 1500 F. and extruded eXamPie, thorium, rare earth Inetai mixtures, z and at 30 feet per minute into /2 inch diameter rods from an s sextrusion container maintained at 1000" F. After re- In dissolving the dispersion hardening eienients in moval from the copper tube the extruded rod, a copper the molten pp eonyentienai ailoy and melting tech alloy product made by the method of the present invenniques as practiced y those Skiiied iii the art, may he tion, had the following tested room temperature properp y The alloying Constituents may contain these ties: 37 percent elongation (%E), 20K s.i. tensile yield amounts and types of impurities normally found therein. Strength (TYS), and 36 i il Strength To obtain the benefits of the solid insoluble second For comparison a copper ll containing 2,44 eight phase material it is essential that the second phase mate- 40 pet-cent misch metal (Comparative example) was eonvehrial he finely and intimately dispersed throughout the tionally cast into 3 inch diameter billets. The billets were solidified PP nietai- Rapid solidification, such as by extruded at 30 feet per minute into /2 inch diameter rods; atoniiling, is a y p in the Preparation of the copper one at 1000 F., one at 1500 F. The rod extruded at alloy Prodlleh The homogeneous Ineit of Copper Contain" 1500" F. had the following tested room temperature proping dispersion hardening material, with or without soluerties; 32% 5 13 Si TYS and 41K Si Ts tion hardening metals and precipitation hardening metals, The copper alloy pellet extrusion product f h presis p y solidified, -g-, y atOIniZing the nioiten nietai ent invention was compared metallographically with the as fine droplets in gas so that droplets solidify theieinconventional ingot extrusion (both extruded at 1500 F.). If desiied, the dTOPiets may he Projected against a The pellet extrusion was only partially recrystallized while latiVeiY 001d metal surface, Preferably Contacting a cold 0 the ingot extrusion was completely recrystallized. This metal surface before the liquidus temperature has been diff is also reheeted in the higher S f the ll Ieflched in the P in Order to Provide more rapid extrusion product. Annealing the pellet extrusion for one cooling and even finer distribution of the second phase at temperatures up to had no etfect on h ri l- In some cases, the alloy may P c001 and structure. Even after annealing at 1900 F. the recrystalsolidify without separation of the second phase. In that lization f the pellet extrusion was incomplete. Grain event, the second phase will generally form and Separate size of the pellet extrusion remained relatively fine (about during or subsequent to wrought operation in which the 1 mil or less) in Spite f annealing. atomized Partieies are P e The data presented show that the method of the present on ceri'ying out rapid solidification by atemizing into invention produces a fine dispersion of solid insoluble a gas environment, it is desirable to utilize pellets small second phase, ie, dispersion hardening, which inhibits enough to p through a 100 mesh sieve Standard recrystallization and grain growth, and has high resistance Sieve series) although pellets as course as about 20 mesh to d f tion at l t d temperature, e g 1000 F, are satisfactory. Use of such fine pellets assures sufii- Further, the pellet extrusion (Example 1) and the eient dispersion of the second Phase material during comparative example were measured for creep resistance solidification of the pellet. The pellets may be collected at elevated temperatures. Table I shows the results of such in water below the gase environment but this is genercreep tests.

TABLE I Percent creep at- Tcn1p., Time, Example N0. F. hrs. 5K s.i. 7.5K s.i. 11.5K s.i. 15K 5.1

The alloy made of the present invention shows substantially improved high temperature creep properties over the conventional alloy. For instance the comparative example had 3.26% creep after 1000 hours at 600 F. while Example 1 had only 0.16% creep.

EXAMPLES 2-5 Various copper alloys containing solid insoluble second phase were melted and atomized into discrete particles by splattering the droplets onto a cold, metallic surface. The resultant particles were extruded from a inch diameter container into a A inch diameter rod at about 1450 F. The rods made by the method of the present invention were tested at room and elevated temperatures. Table II reports various properties of these alloys including %E, TS, yield strength (YS), and electrical conductivity.

For comparison purposes a copper base alloy was prepared and cast into a 3 inch diameter billet which was then extruded into a A inch diameter rod at 1450" F.

one dispersion hardening material sufficient to provide upon solidification from about 1 to about volume percent of second phase;

(b) rapidly solidifying the resultant molten copper al loy into pellets containing said dispersion hardening material as a second phase; and

(c) working the pellets to form a high strength, wrought copper alloy product;

such product being further characterized as containing the second phase dispersed therethrough as particles not exceeding 5 microns in maximum dimension.

2. The method of claim 1 employing at least two dispersion hardening materials wherein at least one of said dispersion hardening materials is selected from the group consisting of calcium, titanium, zirconium, thorium and rare earth mixtures; and at least one of said dispersion hardening materials is selected from the group consisting of boron, silicon, phosphorous, arsenic and antimony.

3. The method of claim 1 wherein the amount of dispersed second phase is from about 2 to about 20 volume TABLE II Copper At 1,000 F. Electrical conductivity N ominal YS at conductivity, equivalent, Example No. composition 1 70 F. %E YS TS 10 mhos/.cm. percent Comparative ingot 2.3 Ti, 0.5B 34 5 2 3 Zr 28 33 14 78. 5 3 3 Th 41 5 10 12 4 3MM 4 14 89.5 5 2.3 Ti, 0.513 32 33 20 26 1 Weight percent: balance being essentially copper.

2 Misch metal 35 to 80 weight percent Oe, up to 5 percent non-rare earth metal, balance being other rare earth elements.

3 Heat treated 1 hour at 1,000 F. before testing.

4 Conductivity of elemental copper is 5.85 (10 mhosJcmfl.

The data of the table demonstrates that the method of the present invention produces a copper alloy product which has substantial room temperature and high temperature strength without a significant loss in conductivity. For example, Example 5 has a yield strength of 4 times that of the comparative alloy although the compositions are the same.

In a like manner other dispersion hardeners as that term has been explained and defined in the specification may be dissolved in molten copper and copper alloys including precipitation hardened alloys, the alloy melt rapidly solidified to form pellets, and the resulting pellets worked to form a copper alloy product which has high strength at room and elevated temperatures plus suflicient conductivity.

The method of the present invention having thus been fully described, various modifications thereof will be at once apparent to those skilled in the art. The scope of the invention is to be considered limited only by the breadth of the claims herein appended.

We claim:

1. A method of preparing a high strength, wrought copper alloy product which comprises:

(a) dissolving in molten copper an amount of at least percent and the second phase particle size in the wrought copper alloy product is less than about 1 micron in maximum dimension.

4. The method of claim 1 and including the step of atomizing the molten resultant copper alloy into droplets thereof to provide rapid solidification into said pellets.

5. The method of claim 4 and including the step of projecting the atomized droplets against a cold, conductive surface thereby to solidify said droplets.

6. The method of claim 1 wherein the working of the solidified resultant alloy pellets is carried out by extrusion.

References Cited UNITED STATES PATENTS 3,138,851 6/1964 Radtke et al. 29l82 3,286,334 11/1966 Hay 29527.7

JOHN F. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner US. Cl. X.R. 

